1. Field of the Invention
The invention relates to a medium-load power generating station with an integrated coal gasification plant, with a gas turbine power generating plant part connected to the coal gasification plant, with a steam power generating station part connected to the raw-gas heat exchanger system of the coal gasification plant, and with a methanol synthesis plant.
2. Description of the Prior Art
British Provisional Pat. No. 20 75 124 discloses a power generating plant, in which a gas turbine is supplied with purified gas from a coal gasification plant. The gas turbine drives an electric generator. The exhaust gas heat of the gas turbine is used in this power generating station for generating steam. The steam drives a steam turbine and a further electric generator. Provision is made in this power generating plant to feed part of the purified gas generated to a methanol synthesis plant and to store the methanol produced. The power output of this power generating station can be controlled synchronously with the output of the coal gasification plant. The output of the latter, however, can be controlled in the range of about 75 and 100%, and also with loss of efficiency at 55% of its rated power, if necessary. It is a peculiarity of this power generating station that load peaks are levelled out only by burning previously generated methanol in the gas turbine in addition to the purified gas. Shutting down the power generating station part which is coupled to the coal gasifier requires shutting down the methanol synthesis plant because there are no means for removal of heat from the raw gas.
European Pat. No. 00 38 138 describes a medium-load power generating plant which has two power generating plants which work completely independently of each other. Of these two power generating plants, the first power generating plant, which comprises a steam turbine plant connected to the waste-heat boiler of the gas turbine, is connected to a coal gasification plant. The coal gasification plant is also connected to a plant for generating synthetic fuels. The first power generating plant operates at base load and can be controlled only to the extent of the preceding coal gasification plant. The latter, however, can be controlled economically only in the range of 75 to 100% of its rated load. Its load behavior is determined decisively by that of the coal gasification plant including the air separation plant associated therewith. The second, independent power generating plant levels out the load fluctuations of the electric power production. In it, however, the substantially more expensive, previously generated synthetic fuel is burned. It is a peculiarity of this plant that excess purified gas must be burned off in the event of sudden load drop-off in the power generating station part, until the equilibrium between the production of purified gas the production of synthetic fuel at the new, lower power generating rate is reestablished. This energy loss can assume considerable proportions because regulating-down a larger coal gasification plant can take more than an hour, while the output of a gas turbine can be throttled down in a few minutes. When levelling-out load peaks as well as in the fast starting-up of this power generating plant, the relatively expensive previously generated fuel must be burned in the second independent power generating plant. This must be done until a power equilibrium is established again.